In general, a coupler apparatus is constituted by arranging a coupling element and a ground plane, each of which is obtained by forming a conductive material into a tabular shape, to face each other. Further, in the coupler apparatus on a transmission side, an electromagnetic field is generated around the coupler apparatus by feeding a signal to a portion between the coupling element and the ground plane to generate an electric current in the coupling element, thereby producing electromagnetic coupling between this coupler apparatus and a coupler apparatus on a reception side. In the coupler apparatus on the reception side, the above-described signal can be fetched as a potential difference between the coupling element and the ground plane when the electric current is generated in the coupling element based on the produced electromagnetic coupling.
In the coupler apparatus, a tabular dielectric may be arranged between the coupling element and the ground plane in some cases to support the coupling element and the ground plane.
It has been desired to increase a performance of coupling between such a coupler apparatus and another coupling apparatus.